Multiband radio receiver



May 4, 1948. A. c. MATTHEWS 2,441,028

MULTIBAND RADIO RECEIVER Filed March 14, 1945 INVENToR.

Patented May 4, 1943 YfrENfr .MULTIBAND RADIG. TREEEIVER Alfred"C. Matthews, Fox chase'Manon'Pa., as-v signer, `by 'mesne assignments, .to `FhilcoCorporation, Phiiadelphi VPennsylvania Pa., 'a vcorporation "of application March i4, i945, serial4 No; 582,719

5 Claims. 1

This invention relatsjto 'improvements in multibandradio receivers. More particularly, theinvention has to fdo with a novel .circuit arrangement `by means .of .which the switching of an"y automatic .volume control' circuit may be effectedfsimultaneousw with the band switching operation, withouttheuse of additional switches or. switch` contacts.

:Infmulti-bandrrado receivers it is frequently desirable toapply. automaticvolumecontrol voltage toa certainmumber-of stagesin .one band, andto a different numbenofstageslin another. Thus, for example,.in.the broadcast bano` it may be .desirable toappl-y an automatic volume control-voltage to alll carrier frequency stages (i. e., radio-frequency converter, and intermediate frequency) whereas in laf-high .Y frequency band it may .be .desirable ilo-apply the automatic frequency control-voltage vto only iaaiew ofthe carrier frequency. stages, AIt is known, for example, that in-` certain highfrequency: bandsr improved reception is obtainedif the rst, carrier frequency stage is operated at-substantia11y full gain throughout, irrespectivefofsignal strength. So far as I am aware, ,practical @circuits for `effecting such changesinautomatic volumercontrol distribution have heretofore `requiredf'the 'use of additional switches! orswitchrcontacts.

.Itis the'principaltobjectfof the present inventionto provide. means :ifor effecting `such` changes inautomatic volumecontrol distribution Without theu'sezof. additional-switchesor switch contacts.

It is another object of the invention. to'. provide a simple and inexpensive-switchingarrangement for :controlling :both bandselecti'oni and automatic volume' control .:distribution, Without .'.cleleteriously aiectingfreception;in'eitherrband;

Theseriandxother objects of thefinvention, and the v.manner which :they are attained, :will appear -fromthe 'following` detailed description and the accompanying- =.:draw-ing in 'which f the single vgure lis a partly f. diagrammatic, partly schematic,l illustration. of ai multi-band radio receiverv constructediin accordance with the principlesf of l#the` invention.v

In :the drawing there.' is: illustrated, by way' of example,` aY two-band xradio; receiver adapted to receive .signals .1 in thef standard broadcast band and-infaeshort-wave (highnfrequency) band. The high frequency band-"may- :bef.a'daptecl for the reception :of either tamplitude `vmodulated or frequency modulated Esignals,,dependingv upon the particular requirements; 'Ihereceiver; aside from the subject-matter of Lthei present invention, is conventional, and comprises a, broadcast band converter and intermediate .i frequency .arnplirV stages il, and .a .detector ,and .-fautornaticV .-volu-ine" control s'tagel Band switching) inthe'frequency converter stage, may bex accompli-shedin cn'ven! tional. manner'. by means, of theban'd switch L6'.

The Yloop antenna' Ifis` tuned yin conventional:

. manner .by means .of .av..coup1ed.resonant circuit* comprisingfthe. inductaiice coil 'Land the .variable tuningnondensen; The high-.frequencyantenna.

circuit, which` vincludes .the'. .dipole lZZand .,.thescou-A pling coil Si, is tuned' by means of aresonanti denser. II in .thettuning of means employed. in -the freguencv..convertenstaec.v .Usually .the .condenser y I I the broadcast.loza.rid..tuningn is Small fomrare f condenser ,8. Onf-the.

are not widelyl-separatedin frequency,-toQelilrii-r natethe. condensereentirely.,.and-.tousel ther-conboth bands.

Thetwo -inductancecoil-s izand I0 faffreacon-n i nested in series betweemcontrolggrid 12v .of .peril-'iy tode I3. and `thechlassis- (ground), ory nthensuit- 1 able .point ot xedrpotential. ..Gonnection.heijlsffeenL the ,coilsl 'I- andA IIJj is byrineans-.oftthellV Ciblockf ing condenser Id. l :'Iheimperia,nceeofathisrconf` denser t-at signal.- @frequencies :should .bje esmalh From thestandpointoi rbest ,desigmtnefcondenser iii-.is preferably inserted-iat` the pointu-shown, f'It ever, that alternatively .this @condensei1 maw-be inserted. at either .or the points-designatedr-:caridfiy.

-An a automatic y"volume control :voltage forrtthe in the art that,A alternatively; this," voltage "11m end) ofithepcoiilo; or ,atany intermedi thereonl' lMoreover,'ifthecodenser [k'ILb t mais; ferredto lthe point .1l/.the .automatic yolum .conf

trol voltage may, if-fdesired,:beintrodueedeatlmcf f Automatic volume `Fcom/1101"fvoltages fronti the?.y

vgrid I2 of pentode I3.

converter and intermediate frequency amplier stages 4 by way of the conductor I9.`

Band switching in the input circuits to the radio frequency amplier stage 3 is accomplished by means of a switch 20 which may be ganged with (or be a part of) the band switch E. In the open position (shown) thereceiver is adapted for operation in the'broadcast band, tuning being accomplished through the agency of the variable condenser 8. In this position the high frequency coil II! is eiectively in series between the high potential end of the resonant circuit 'I-8 and However, at broadcast band frequencies the inductance of coil I is negligible and its effect on the circuit is likewise negligible. The small high frequency tuning condenser I I is now effectively in shunt with the tuning condenser 8 and aids in tuning the coil 1. p When the switch is in its closed position, the loop antenna circuit is effectively shorted, while at the Sametime the high frequency resonant circuit comprising the inductance coil I0 and tuning condenser II is completed, permitting the reception of signals in the high frequency band as sup-1 plied by the dipole V2. It is an important feature of the invention that in the high frequency, or closed, position of the switch 20, the said switch is at the low potential end of the resonant circuit lit-II, rather than at the high potential end thereof. In this position the distributed capacity ofthe switch to ground doe-s not appear in shunt with the tuning condenser II and hence does not diminish or dilute thetuningrange of the condenser.

By virtue 'of the connections recited hereinbefore an arrangement has been provided wherein tlie'single switch 2G serves simultaneously as a band switching means, and asa means for providing an yautomatic volume control voltage for the amplier 3- during broadcast reception and for' vremoving said voltage during reception in the high frequency band. Thus it will be observed that during'broadcast reception, with the switch 20 open, automatic volume control voltage is applied to the control grid I2 of pentode I3 by way of the path I5, I6, II, I8, and the coil I0. On thc other! hand, during highifrequency reception, when the switchZ is closed, the left-hand end of the--series resistor I8 isgrounded through the switch 20, thus removing the automatic volume control voltage from the pentode I3. At the same time, the blocking condenser I4 and the series resistor I8 arecompletely removed from association with theresonant circuit- III-II thus reducing circuit losses in the frequency `band where small los'sesware particularly to beV avoided.

lIn general the resistance of the series resistor IB should be high, e. g., of the order of a half megohm or more, so that the closing of the switch 2U will not substantially reduce the magnitude of theautomatic volume control voltage supplied to the remaining carrier frequency stages 4 by way ofthe conductor I9. On they other hand, there ccY may be instances when it is desired to reduce the magnitude ofthe automatic volume control voltage` applied to the stages 4 during high frequency reception. plished by inserting the resistor 'I6 in the automatic volume control path as shown. Closing of the 'switch 20 willv then reduce the voltage suppliedto the, conductor I9 by'afactor depending upon the ratio of resistors IGand I8, as will be evident'to those skilled in the art.

In the interests of simplicity the invention has been illustrated and described as applied to a single stage in a conventional radio receiver. It will be evident, of course, that the invention is similarly applicable to other stages, or to more than one stage. The invention is capable of still other modification within the scope of the appended claims,

Iclaim:

l. In a multi-band radio receiver,a band-selecting switch, a source of automatic volume control voltage, a vacuum tube having at least a control grid, an anode and a cathode, a rst coil adapted for operation over a predetermined wave band, a second coil adapted for operation over a dilerent wave band, means for tuning said coils over their respective wave bands, a direct-current connection between the high potential end of said second coil and the control grid of said vacuum tube, a connection between the low potential end of said second coil and the high potential end of said rst coil, a connection between the low potential end of said first coil and said cathode, one of said two last-named connections including a capacitor, a direct-current connection between said source of automatic volume control voltage and the low potential end of said second coil, and switch contact elements operative in one position of said band-selecting switch to effect a direct-current connection between the low potential end of said second coil and said cathode, and operative in anotherposition of said band switch to break-said last-named connection.

2. In a multi-band radio receiver, a source of automatic volume control voltage, a vacuum tube operating at a lcarrier frequency, a first coil adapted for operation overa band, a second coil'adapted for operation over a higher frequency wave band', Vmeans for tuning said coils over their respective wave bands, a direct-current connection between the high potential end of said secondcoil and the control grid of said vacuum tube; a, connection between the low potential endo said second coil and the high potential end of said first coil, a connection between the low potential'end of said first coil and a point of substantially fixed potential, one of said two last-named'connections including a capacitor, a high-resistance direct-current connection between said'so'ur'ceof automatic volume control voltage and the "lowpotential end of said second coil, and a switch connected between the low potential end of said'second coil and a point of substantially'xed potential, said switch being adjustable to open-circuitand closed-circuit positions selectively. Y

3. In a multi-band radio receiver, a first carrier frequency stage including a vacuum tube having a control grid, a subsequent.' carrier frequency stage, a source ofv automatic volume control voltage, a, band-selecting switch 'for conditioning said receiver for the reception of signals in either one A of a plurality of wave bands, a nrst coil adapted for operation over a predetermined wave band, a second coil adapted' for operation over a diierent wave band, means'for tuning said coils over their respective wave bands, a direct-current connection between the high potential end of said This may be conveniently' accomsecondcoil and the control grid of said vacuum tube, a capacitor connectedbetween the low potential endof the said second coil and the high potential end of said rst coil, a connection between the low potential end of said rst coil and a point of Xed potential, a direct-current connection between said source of automatic volume control voltage and the gain control element of said subsequent stage, a, high resistance series repredetermined wave sistor connected in a direct-current path between said source and the low potential end of said second coil, and switch contact elements operative in one position of said band-selecting switch to connect the low potential end of said second coil to a point of fixed potential, and operative in another position of said band switch to break said last-named connection.

4. In a multi-band radio receiver, a first carrier frequency stage including a vacuum tube having a control grid, a subsequent carrier frequency stage, a source of automatic volume control voltage, a band-selecting switch for conditioning said receiver for the reception of signals in either one of a plurality of wave bands, a first coil adapted for operation over a predetermined wave band, a second coil adapted for operation over a different wave band, means for tuning said coils over their respective wave bands, a direct-current connection between the high potential end of said second coil and the control grid of said vacuum tube, a capacitor connected between the low potential end of the said second coil and the high potential end of said rst coil, a connection between the low potential end of said rst coil and a point of xed potential, a pair of series connected high resistance elements connected in a direct-current path between said source and the low potential end of said second coil, a directcurrent connectionbetween the junction of said resistance elements and the gain control element of said subsequent stage, and switch contact elements operative in one position of said band-selecting switch to connect the low potential end of said second coil to a point of xed potential, and operative in another position of said band switch to break said last-named connection.

5. In a multi-band radio receiver, a source of automatic volume control voltage, a vacuum tube having at least a grid, a cathode, and an anode, a rst coil adapted for operation over a predetermined wave band, a second coil adapted for operation over a different wave band, means for tuning said coils over their respective wave bands, a capacitor, means connecting said coils and said capacitor in series between said grid and said cathode, a direct-current connection between said source and said grid, and a single-pole-singlethrow switch connected between said cathode and a point intermediate said coils, said switch, in its closed position, providing a direct-current short-circuit across Isaid source while simultaneously providing an alternating-current short-circuit across one of said coils.

ALFRED C'. MATTHEWS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number 

